source: mainline/kernel/arch/arm32/src/fpu_context.c@ 46a6a5d

/*
 * Copyright (c) 2012 Jan Vesely
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup arm32
 * @{
 */
/** @file
 *  @brief arm32 FPU context
 */

#include <fpu_context.h>
#include <arch.h>
#include <arch/types.h>
#include <cpu.h>

#define FPSID_IMPLEMENTER(r)   ((r) >> 24)
#define FPSID_SW_ONLY_FLAG   (1 << 23)
#define FPSID_SUBACHITECTURE(r)   (((r) >> 16) & 0x7f)
#define FPSID_PART_NUMBER(r)   (((r) >> 8) & 0xff)
#define FPSID_VARIANT(r)   (((r) >> 4) 0xf)
#define FPSID_REVISION(r)   (((r) >> 0) 0xf)


enum {
        FPU_VFPv1 = 0x00,
        FPU_VFPv2_COMMONv1 = 0x01,
        FPU_VFPv3_COMMONv2 = 0x02,
        FPU_VFPv3_NO_COMMON = 0x3, /* Does not support fpu exc. traps */
        FPU_VFPv3_COMMONv3 = 0x4,
};

enum {
        FPEXC_EX_FLAG = (1 << 31),
        FPEXC_ENABLED_FLAG = (1 << 30),
};

/** ARM Architecture Reference Manual ch. B4.1.58, p. B$-1551 */
enum {
        FPSCR_N_FLAG = (1 << 31),
        FPSCR_Z_FLAG = (1 << 30),
        FPSCR_C_FLAG = (1 << 29),
        FPSCR_V_FLAG = (1 << 28),
        FPSCR_QC_FLAG = (1 << 27),
        FPSCR_AHP_FLAG = (1 << 26),
        FPSCR_DN_FLAG = (1 << 25),
        FPSCR_FZ_FLAG = (1 << 24),
        FPSCR_ROUND_MODE_MASK = (0x3 << 22),
        FPSCR_ROUND_TO_NEAREST = (0x0 << 22),
        FPSCR_ROUND_TO_POS_INF = (0x1 << 22),
        FPSCR_ROUND_TO_NEG_INF = (0x2 << 22),
        FPSCR_ROUND_TO_ZERO = (0x3 << 22),
        FPSCR_STRIDE_MASK = (0x3 << 20),
        FPSCR_STRIDE_SHIFT = 20,
        FPSCR_LEN_MASK = (0x7 << 16),
        FPSCR_LEN_SHIFT = 16,
        FPSCR_DENORMAL_EN_FLAG = (1 << 15),
        FPSCR_INEXACT_EN_FLAG = (1 << 12),
        FPSCR_UNDERFLOW_EN_FLAG = (1 << 11),
        FPSCR_OVERFLOW_EN_FLAG = (1 << 10),
        FPSCR_ZERO_DIV_EN_FLAG = (1 << 9),
        FPSCR_INVALID_OP_EN_FLAG = (1 << 8),
        FPSCR_DENORMAL_FLAG = (1 << 7),
        FPSCR_INEXACT_FLAG = (1 << 4),
        FPSCR_UNDERFLOW_FLAG = (1 << 3),
        FPSCR_OVERLOW_FLAG = (1 << 2),
        FPSCR_DIV_ZERO_FLAG = (1 << 1),
        FPSCR_INVALID_OP_FLAG = (1 << 0),

        FPSCR_EN_ALL = FPSCR_DENORMAL_EN_FLAG | FPSCR_INEXACT_EN_FLAG | FPSCR_UNDERFLOW_EN_FLAG | FPSCR_OVERFLOW_EN_FLAG | FPSCR_ZERO_DIV_EN_FLAG | FPSCR_INVALID_OP_EN_FLAG,
};

static inline uint32_t fpscr_read()
{
        uint32_t reg;
        asm volatile (
                "vmrs %0, fpscr\n"
                :"=r" (reg)::
        );
        return reg;
}

static inline void fpscr_write(uint32_t val)
{
        asm volatile (
                "vmsr fpscr, %0\n"
                ::"r" (val):
        );
}

static inline uint32_t fpexc_read()
{
        uint32_t reg;
        asm volatile (
                "vmrs %0, fpexc\n"
                :"=r" (reg)::
        );
        return reg;
}

static inline void fpexc_write(uint32_t val)
{
        asm volatile (
                "vmsr fpexc, %0\n"
                ::"r" (val):
        );
}

static void (*save_context)(fpu_context_t *ctx);
static void (*restore_context)(fpu_context_t *ctx);

/** Saves 32 single precision fpu registers.
 * @param ctx FPU context area.
 * Used by VFPv1
 */
static void fpu_context_save_s32(fpu_context_t *ctx)
{
        asm volatile (
                "vmrs r1, fpexc\n"
                "vmrs r2, fpscr\n"
                "stmia %0!, {r1, r2}\n"
                "vstmia %0!, {s0-s31}\n"
                ::"r" (ctx): "r1","r2","memory"
        );
}

/** Restores 32 single precision fpu registers.
 * @param ctx FPU context area.
 * Used by VFPv1
 */
static void fpu_context_restore_s32(fpu_context_t *ctx)
{
        asm volatile (
                "ldmia %0!, {r1, r2}\n"
                "vmsr fpexc, r1\n"
                "vmsr fpscr, r2\n"
                "vldmia %0!, {s0-s31}\n"
                ::"r" (ctx): "r1","r2"
        );
}

/** Saves 16 double precision fpu registers.
 * @param ctx FPU context area.
 * Used by VFPv2, VFPv3-d16, and VFPv4-d16.
 */
static void fpu_context_save_d16(fpu_context_t *ctx)
{
        asm volatile (
                "vmrs r1, fpexc\n"
                "vmrs r2, fpscr\n"
                "stmia %0!, {r1, r2}\n"
                "vstmia %0!, {d0-d15}\n"
                ::"r" (ctx): "r1","r2","memory"
        );
}

/** Restores 16 double precision fpu registers.
 * @param ctx FPU context area.
 * Used by VFPv2, VFPv3-d16, and VFPv4-d16.
 */
static void fpu_context_restore_d16(fpu_context_t *ctx)
{
        asm volatile (
                "ldmia %0!, {r1, r2}\n"
                "vmsr fpexc, r1\n"
                "vmsr fpscr, r2\n"
                "vldmia %0!, {d0-d15}\n"
                ::"r" (ctx): "r1","r2"
        );
}

/** Saves 32 double precision fpu registers.
 * @param ctx FPU context area.
 * Used by VFPv3-d32, VFPv4-d32, and advanced SIMD.
 */
static void fpu_context_save_d32(fpu_context_t *ctx)
{
        asm volatile (
                "vmrs r1, fpexc\n"
                "stmia %0!, {r1}\n"
                "vmrs r1, fpscr\n"
                "stmia %0!, {r1}\n"
                "vstmia %0!, {d0-d15}\n"
                "vstmia %0!, {d16-d31}\n"
                ::"r" (ctx): "r1","memory"
        );
}

/** Restores 32 double precision fpu registers.
 * @param ctx FPU context area.
 * Used by VFPv3-d32, VFPv4-d32, and advanced SIMD.
 */
static void fpu_context_restore_d32(fpu_context_t *ctx)
{
        asm volatile (
                "ldmia %0!, {r1}\n"
                "vmsr fpexc, r1\n"
                "ldmia %0!, {r1}\n"
                "vmsr fpscr, r1\n"
                "vldmia %0!, {d0-d15}\n"
                "vldmia %0!, {d16-d31}\n"
                ::"r" (ctx): "r1"
        );
}

void fpu_init(void)
{
        /* Clear all fpu flags */
        fpexc_write(0);
        fpu_enable();
        /* Mask all exception traps,
         * The bits are RAZ/WI on archs that don't support fpu exc traps.
         */
        fpscr_write(fpscr_read() & ~FPSCR_EN_ALL);
}

void fpu_setup(void)
{
        uint32_t fpsid = 0;
        asm volatile (
                "vmrs %0, fpsid\n"
                :"=r"(fpsid)::
        );
        if (fpsid & FPSID_SW_ONLY_FLAG) {
                printf("No FPU avaiable\n");
                return;
        }
        switch (FPSID_SUBACHITECTURE(fpsid))
        {
        case FPU_VFPv1:
                printf("Detected VFPv1\n");
                save_context = fpu_context_save_s32;
                restore_context = fpu_context_restore_s32;
                break;
        case FPU_VFPv2_COMMONv1:
                printf("Detected VFPv2\n");
                save_context = fpu_context_save_d16;
                restore_context = fpu_context_restore_d16;
                break;
        case FPU_VFPv3_COMMONv2:
        case FPU_VFPv3_NO_COMMON:
        case FPU_VFPv3_COMMONv3: {
                uint32_t mvfr0 = 0;
                asm volatile (
                        "vmrs %0,mvfr0\n"
                        :"=r"(mvfr0)::
                );
                /* See page B4-1637 */
                if ((mvfr0 & 0xf) == 0x1) {
                        printf("Detected VFPv3+ with 16 regs\n");
                        save_context = fpu_context_save_d16;
                        restore_context = fpu_context_restore_d16;
                } else {
                        printf("Detected VFPv3+ with 32 regs\n");
                        save_context = fpu_context_save_d32;
                        restore_context = fpu_context_restore_d32;
                }
                break;
        }

        }
}

bool handle_if_fpu_exception(void)
{
        const uint32_t fpexc = fpexc_read();
        if (fpexc & FPEXC_ENABLED_FLAG) {
                const uint32_t fpscr = fpscr_read();
                printf("FPU exception\n"
                    "\tFPEXC: %" PRIx32 " FPSCR: %" PRIx32 "\n", fpexc, fpscr);
                return false;
        }
#ifdef CONFIG_FPU_LAZY
        scheduler_fpu_lazy_request();
        return true;
#else
        return false;
#endif
}

void fpu_enable(void)
{
        /* Enable FPU instructions */
        fpexc_write(fpexc_read() | FPEXC_ENABLED_FLAG);
}

void fpu_disable(void)
{
        /* Disable FPU instructions */
        fpexc_write(fpexc_read() & ~FPEXC_ENABLED_FLAG);
}

void fpu_context_save(fpu_context_t *ctx)
{
        const uint32_t fpexc = fpexc_read();

        if (fpexc & FPEXC_EX_FLAG) {
                printf("EX FPU flag is on, things will fail\n");
                //TODO implement common subarch context saving
        }
        if (save_context)
                save_context(ctx);
}

void fpu_context_restore(fpu_context_t *ctx)
{
        if (restore_context)
                restore_context(ctx);
}